Heating Effects in a Liquid Metal Ion Source

A reassessment is made of the heating occurring at the anode of a liquid metal ion source (LMIS), in the light of new microscopic observations. These observations concern the liquid cone that constitutes the basis of a LMIS, and forms either at the apex of a solid needle, or at the end of a capillary. It is now revealed that the apex region of the cone is in the form of a cusp, or jet, even at very low currents. As far as ohmic heating is concerned, the calculation is conclusive for low currents: no heating occurs at the anode; for high currents ( approx 50-100 mu A), substantial heating is conceivable, if a long, very thin, cylindrical jet exists at the apex of the anode. The answer to the problem of external heating, in the form of electrons bombarding the anode, is not quite conclusive; this is because of the impossibility of correctly assessing the electron flux entering the anode (although experimental evidence is more inclined towards suggesting a lack of available power for substantial heating). However, is would appear to be a definite conclusion (not altered by the new observations) that for reasons of self-consistency field-ionisation of thermally released atoms cannot be a significant ion emission mechanism. 14 ref.--AA